Dampening roll cover and its use in lithographic printing



1965 s. G. PETERSON ET AL 3,229,351

DAMPENING ROLL COVER AND ITS USE IN LITHOGRAPHIC PRINTING Filed July 16,1962 5) mwzawb WM,

United States Patent 3,229,351 DAMPENING ROLL COVER AND ITS USE INLITHOGRAPHIC PRINTING Stanley G. Peterson, Minneapolis, and Leonard W.Sachi, St. Paul, Minn., assignors to Minnesota Mining and ManufacturingCompany, St. Paul, Minn, a corporaticn of Delaware Filed July 16, 1962,Ser. No. 210,126 15 (Ilairns. (Cl. 29-1295) This invention relates to anew and useful dampening roll cover for use in lithographic printing. Inone aspect, this invention relates to a non-woven dampening roll coverwhich is economical to manufacture and also both convenient andefiicient to use in lithographic printing processes.

In lithographic printing, it is necessary to selectively wet the surfaceof a printing plate with water before the application of oil-basedprinting inks. To selectively wet a lithographic printing plate, a clothcovered dampening roll or rolls has heretofore conventionally been used.These cloth covered rolls are moistened with water and thereafter passedover the surface of the printing plate, the wetting action beingachieved by the deposit of water pressed out of the porous cloth uponthe plate surface. With such cloth covered rolls, however, it has been aproblem to uniformly wet the printing surface without also depositingforeign substances, such as lint, from the cloth cover. Moreover, thecloth cannot be readily cleaned, and the operator of the lithograph'cpress must consequently compensate for the variable wetting actionfrequently obtained with use of such cloth covers. Such covers have beenapplied with difficulty to the roller by securing the cover at each endwith stitching. The worn covers are later removed by cutting away thestitching at each end. In actual use, cloth covered rolls tend tocompact, thus changing in porosity as well as in diameter during theprinting run. Because the proper Water-ink balance must be maintainedfor optimum results, frequent adjustments on the printing press haveoften been necessary to compensate for these changes.

Convolutely wrapping multiple layers of non-woven fabrics about thedampening roll has also been suggested, but such covers have an outertrailing edge that can disrupt the desired uniformity of the dampeningrol surface. Moreover, covers of this type are difiicult to attachsnugly over the roll.

It is therefore an object of this invention to provide a non-wovendampening roll cover of improved design for use in lithographic printingand a process for its manufacture.

Another object of this invention is to provide a seamless dampening rollcover which is convenient and economical to use and which fits snugly onthe roll.

Still another object of this invention is to provide a dampening rollcover which is more capable of applying in controllable fashion auniform quantity of water under a lithographic plate with a minimum ofadjustment durin g the printing run.

Other objects of this invention will be apparent from the followingdescription.

In accordance with this invention, the new and useful dampening rollcover comprises a seamless, cohesive, porous, hygroscopic, non-wovencylindrical sleeve having a uniform surface texture, said sleeve beingcomprised of hydrophilic, randomly disposed, fibers which (1) aresubstantially water insoluble at temperatures below about 100 F.,preferably below 170 F., (2) can be longitudinally expanded, preferablyat least 3%, when water wetted, (3) have dimensional stability when dry,and

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(4) longitudinally contract from their expanded state when water wetted,the sleeve also being resistant to tearing, abrasion and fiberdisorientation when water wetted.

Non-woven webs and fabrics of a Wide variety of materials are wellknown, and the preparation or selection of a propriate non-woven webs orfabrics containing fibers with the aforementioned properties can readilybe determined by those skilled in the art. The following simple testprocedure can be used to determine the suitability of any fibrousmaterial or materials in non-woven form.

After the hydrophilic properties of the non-woven sample are positivelyestablished (its. oleophobic when water wetted), a 2-inch by 3-inchspecimen is cut from the sample. Marks are made /2-inch from each end, 2inches apart. The specimen is then wetted thoroughly with water, andeach end is clamped in one jaw of a suitable tester, such as a tensiletest device. The jaws are separated at a rate of one-inch per minuteuntil an elongation of at least 2 percent is achieved. The specimen isthen permitted to dry in this expanded condition. The dry specimen isthen removed from the tester and placed in an oven at 70 F. and 10%relative humidity for at least 24 hours. No significant contractionshould occur during this exposure. The specimen is then again thoroughlywetted with water, and the contraction is measured. The rewettedspecimen should recover at least about 30 percent of its totalexpansion.

If a single specimen, swatch or layer of non-woven material does notmeet the above test requirements, several layers of the same ordifferent non-woven material may be bonded together to improve itsperformance. By using a hydrophilic fiber and/or a resin which is heatfusible or heat and moisture fusible in conjunction with the otherhydrophilic fibers in the non-woven web, several layers of the web maybe bonded together by the application of either heat alone or heat andmoisture while subjecting the several layers to pressure in a suitabledevice, such as a heated hydraulic platen press. The particularconditions of heat, moisture and pressure depend, of course, on thefibers or resins employed. Preferably, the pressure should be sufiicientto compress the several layers to about 20 percent of their originalcombined thickness.

A particularly preferred class of hydrophilic fibrous material for thenon-woven web is the polyvinyl alcohol fibers, especially thosepolyvinyl alcohol fibers with a denier from about 0.5 to about 6 and anindividual average fiber length of from about 0.25 to about 2 inches(preferably 0.5 to 1.5). Polyvinyl alcohol fibers are available invarious grades, depending on their solubility characteristics in hotwater. Other useful heat fusible fibers, i.e. fibers capable of beingcohered or bonded to each other upon application of heat and pressurewith or without the presence of moisture, include the polypyrrolidonefibers. In general, the inclusion of additional hydrophilic fibers, notnecessarily heat fusible, in the non-woven web is preferred. Fibers suchas cotton, regenerated cellulose, viscose rayon, cellulose acetate rayonand other rayons, may'thus also be incorporated to modify the propertiesof the non-woven web and hence of the sleeve, e.g. increase strength andhydrogroscopic properties, etc. Saponified cellulose acetate fibers,particularly those in which cellulose acetate fibers are saponified intheir oriented condition during their manufacture (e.g. Fortisan fibers)and having a denier from about 0.5 to about 3 and an average fiberlength of from about 0.25 to about 2 inches (preferably 0.5 to 1.5), incombination with at least 20 weight percent of polyvinyl alcohol fibersprovide a non-woven material having outstanding properties when used asa dampening roll cover in accordance with this invention. Fortisanfibers are described in Man-Made Fibers, R.

. 3 W. Moncrieff (J. Wiley and Sons, 1957), pp. 221-223. Occasionally,it is found that a small amount of a binder, e.g. a water solublepolyvinyl alcohol resin, may be applied, preferably from solution, tothe dry fibers in the preparation of the non-woven material to assist inbonding the fibers together into a cohesive web. Usually a maximum ofabout weight percent, preferably less than about 2 weight percent, ofthe non-woven web is binder, particularly when the more water solublebinders are employed.

The preparation of non-woven webs from dry fibers, either with orwithout additional binder materials, may be carried out by conventionalmeans, e.g. a Rando-Webber machine, etc. The average fiber lengths of0.5 to 2 inches are useful in the dry process for preparing non-wovenwebs. Non-woven webs of 15 mils maximum thickness, preferably of milsmaximum thickness, are generally most useful.

The process of manufacturing the non-woven sleeve of this invention canbetter be understood by reference to the drawings.

FIGURE 1 shows the step of wrapping one or more turns of a strip ofnon-woven web material 1 around a mandrel 2. In FIGURE 2 a wetted curingtape, i.e. a tape which shrinks upon drying, such as the nylon cure tapecommonly used in the manufacture of rubber rolls, is wrapped tightlyabout the mandrel over the multiple layers of non-woven web. This isthen heated in the presence of moisture, e.g. a moist atmosphere, to atemperature sufficient to elfect at least a partial fusion of some ofthe nonwoven fibers to each other, e.g. 200 F. to 300 F. for polyvinylalcohol fibers and to produce a cohesive sleeve. As the fusion occurs,the layers of non-woven web are simultaneously placed under radialcompression due to the contraction of the cure tape. Other means forobtaining the desired radial compression can be used in place of curetape, as will be readily appreciated. In general, a radial compressionto a maximum of 50 percent of the original thickness of the non-wovenlayers is preferred to obtain a high density product, although theamount of compression may vary widely depending on the original densityof the non-woven web. After drying, the cure tape is removed and, ifdesired, the exposed exterior surface 3 is sanded to remove surfaceirregularities. Such sanding may be accomplished by rotating the sleeveand mandrel at high speed while contacting the surface with a rotatingsanding wheel 4, as shown in FIGURE 3.

The sleeve is then slipped over an expandable mandrel 5, as shown inFIGURE 4, wetted with Water and mechanically expanded at least about 2percent in diameter, preferably about 5 percent. The expanded sleeve isdried in its expanded condition, in which state the sleeve retains itsexpanded dimensions and is ready for use as dampening roll cover. Theexpandable mandrel is then removed. The dry sleeve may readily beslipped over a dampening roller 6 as shown in FIGURE 5. Upon moisteningwith water, the sleeve contracts to the dimensions of the roller andtightly adheres to its surface. It is therefore an essential property ofthe mat material used in making the sleeve of this invention that it iscapable of being expanded in its wetted condition, that it retain itsexpanded dimensions after drying, and that it shrinks significantly uponrewetting. The operation of the sleeve covered dampening roller is shownin FIGURE 6. A curved printing plate 7 on rotating printing roll 8 iswetted by the covered dampening roller 9 which is also in contact withvibrator roll 10. The vibrator roll is in turn contacted by ductor roll11 and fountain roll 12, which transfers moisture from the fountainreservoir 13. This technique is conventional in the lithographic art.

To illustrate this procedure, a dry ll-inch by 32 /2- inch sheet ofnon-woven web material containing 50 weight percent of Fortisan 36 fiber(resaponified cellulose acetate rayon product, tensile strength of155,000 p.s.i., specific gravity of 1.52, a product of CelaneseCorporation of America) and 50 weight percent of substantially waterinsoluble polyvinyl alcohol fiber (unacetylyzed and non-heat treated)along with a small amount of water soluble polyvinyl resin (Elvanol7260, product of E. I. du Pont de Nemours and Co.), was wrappedconvolutely around a 2.000 inch diameter mandrel. Exactly five wraps orconvolutions were made so that the trailing edge was directly over theleading edge, though separated by four layers of the web. This wrappedmandrel was then spirally overwrapped with a wet nylon cure tape, andthe overwrapped mandrel was placed in an open steam autoclave at 40pounds per square inch gauge pressure for 15 minutes at 285 F. Afterremoval from the autoclave, the cure tape was allowed to dry before itwas removed, leaving the five layers of web cohered into a dense,uniform, unitary sleeve. This sleeve was then sanded with 150 gritsandpaper to remove the cure tape pattern on the sleeve surface. Thesleeve was removed from the mandrel and was slipped over a mechanicalexpander consisting of a 2-inch outside diameter pipe, split along itsaxis into two sections. After moistening the sleeve with water, wedge-swere driven between the pipe sections at each pipe end to increase thecircumference of the sleeve and increase its diameter to 2.100 inch. Thesleeve was dried in this expanded condition and was removed in thisdimensionally stable state from the expanding mandrel. The dry sleevewas readily slipped over a lithographic press dampening roller of 2.055inch diameter and was wetted with water. The wet sleeve shrunk toconform tightly to the roller surface. Using this covered dampeningroller, several thousand impressions were run on a lithographic presswith an aluminum offset plate imaged in conventional manner. Comparativeruns with cloth covered rolls showed that the non-woven coveringremained cleaner and more lint free and permitted better control of thewater applied to the plate; cleaner copy is therefore possible. Similarresults were obtained with a seamless non-woven sleeve of about weightpercent cellulose acetate rayon fibers and about 20 weight percent ofsubstantially water insoluble polyvinyl alcohol fibers, using only fourwraps of the web, and also with a seamless non-woven sleeve of 50 weightpercent cellulose acetate rayon fibers and 50 weight percent ofpolypyrrolidone fibers (melting point, 265 C.; second order drytransition temperature, 23 C.; wet elongation, 11%). Less satisfactory,though useful, results were obtained with a sleeve of weight percentsubstantially water insoluble polyvinyl alcohol fibers.

The ease of mounting the seamless non-woven sleeves and of theirsubsequent removal is outstanding. Because of the uniform density of thesleeves and their resistance to compacting, less adjustment of the watersupply from the fountain reservoir is required during actual use, andnew sleeves can be used without any significant break-in period. Whendesired, the non-woven sleeves can be readily cleaned with a suitablesolvent without removal from the roll.

Various other embodiments of the present invention will be apparent tothose skilled in the art without departing from the spirit or scopethereof.

We claim:

1. A dampening roll cover which consists of a seamles, porous,hygroscopic, cohesive, wholly non-woven cylindrical sleeve consistingessentially of hydrophilic materials, said sleeve being comprised ofhydrophilic randomly disposed fibers which (1) are substantially waterinsoluble at temperatures below about 100 F.,

(2) can be longitudinally expanded when water wetted,

(3) have dimensional stability in the dry expanded state, and

(4) longitudinally contract from the expanded state When wetted withwater at room temperature, said sleeve further being resistant totearing, abrasion and fiber disorientation when water wetted.

2. The dampening roll cover of claim 1 in which said fibers comprisefrom about 20 to 100 weight percent of polyvinyl alcohol fibers and from0 to about 80 weight percent of cellulosic fibers.

3. The dampening roll cover of claim 1 in which said fibers comprisefrom about 20 to about 80 weight percent of polyvinyl alcohol fibershaving a denier from about 0.5 to about 6 and an average fiber length offrom about 0.5 to about 2 inches, and from about 20 to about 80 weightpercent of cellulose acetate rayon fibers having a denier from about 0.5to about 3 and an average fiber length of from about 0.5 to about 2inches.

4. The dampening roll cover of claim 1 in which said fibers comprisefrom about 20 to about 80 weight percent of polypyrrolidone fibershaving a denier from about 0.5 to about 6 and an average fiber length offrom about 0.5 to about 2 inches, and from about 20 to about 80 Weightpercent of cellulose acetate rayon fibers having a denier from about 0.5to about 3 and an average fiber length of from about 0.5 to about 2inches.

5. The dampening roll cover of claim 1 in which said fibers compriseabout 20 weight percent of polyvinyl alcohol fibers having a denier fromabout 0.5 to about 6 and an average fiber length of from about 0.5 toabout 2 inches, and about 80 weight percent of cellulose acetate rayonfibers having a denier from about 0.5 to about 3 and an average fiberlength of from about 0.5 to about 2 inches.

6. The dampening roll cover of claim 1 in which said fibers compriseabout 50 weight percent of polyvinyl alcohol fibers having a denier fromabout 0.5 to about 6 and an average fiber length of from about 0.5 toabout 2 inches, and about 50 weight percent of cellulose acetate rayonfibers having a denier from about 0.5 to about 3 and an average fiberlength of from about 0.5 to about 2 inches.

7. The dampening roll cover of claim 1 in which said fibers compriseabout 50 weight percent of polypyrrolidone fibers having a denier fromabout 0.5 to about 6 and an average fiber length of from about 0.5 toabout 2 inches, and about 50 weight percent of cellulose acetate rayonfibers having a denier from about 0.5 to about 3 and an average fiberlength of from about 0.5 to about 2 inches.

8. A dampening roll cover which consists of a dry, seamless, porous,hydroscopic, cohesive, wholly nonwoven cylindrical sleeve, consistingessentially of hydrophilic materials, said sleeve being comprised ofhydro philic randomly disposed fibers which (1) are substantially waterinsoluble at temperatures below about 100 F.,

(2) can be longitudinally expanded when water wetted,

(3) have dimensional stability in the dry expanded state, and

(4) longitudinally contract from the expanded state when wetted withwater and room temperature, said sleeve being rapidly and radiallyshrinkable when water Wetted and further being resistant to tearingabrasion and fiber disorientation when water wetted.

9. The dampening roll cover of claim 8 in which said fibers comprisefrom about 20 to 100 weight percent of polyvinyl alcohol fibers and from0 to 80 weight percent of cellulosic fibers.

10. The dampening roll cover of claim 8 in which said fibers comprisefrom about 20 to about 80 weight percent of polyvinyl alcohol fibershaving a denier from about 0.5 to about 6 and an average fiber length offrom about 0.5 to about 2 inches, and from about 20 to about weightpercent of cellulose acetate rayon fibers having a denier from about 0.5to about 3 and an average fiber length of from about 0.5 to about 2inches.

11. The dampening roll cover of claim 8 in which said fibers comprisefrom about 20 to about 80 weight percent of polypyrrolidone fibershaving a denier from about 0.5 to about 6 and an average fiber length offrom about 0.5 to about 2 inches, and from about 20 to about 80 weightpercent of cellulose acetate rayon fibers having a denier from about 0.5to about 3 and an average fiber length of from about 0.5 to about 2inches.

12. The dampening roll cover of claim 8 in which said fibers compriseabout 20 weight percent of polyvinyl alcohol fibers having a denier fromabout 0.5 to about 6 and an average fiber length of from about 0.5 toabout 2 inches, and about 80 weight percent of cellulose acetate rayonfibers having a denier from about 0.5 to about 3 and an average fiberlength of from about 0.5 to about 2 inches.

13. The dampening roll cover of claim 8 in which said fibers compriseabout 50 weight percent of polyvinyl alcohol fibers having a denier fromabout 0.5 to about 6 and an average fiber length of from about 0.5 toabout 2 inches, and about 50 weight percent of cellulose acetate rayonfibers having a denier from about 0.5 to about 3 and an average fiberlength of from about 0.5 to about 2 inches.

14. The dampening roll cover of claim 8 in which said fibers compriseabout 50 weight percent of polypyrrolidone fibers having a denier fromabout 0.5 to about 6 and an average fiber length of from about 0.5 toabout 2 inches, and about 50 weight percent of cellulose acetate rayonfibers having a denier from about 0.5 to about 3 and an average fiberlength of from about 0.5 to about 2 inches.

15. A dampening roll cover which consists of a seamless, porous,hygroscopic, cohesive, wholly non-woven cylindrical sleeve consistingessentially of hydrophilic materials, said sleeve being comprised ofhydrophilic randomly disposed fibers of a material selected from thegroup consisting of polyvinyl alcohol, polypyrrolidone and rayon, whichfibers (1) are substantially water insoluble at temperatures below aboutF.,

(2) can be longitudinally expanded when Water wetted,

(3) have dimensional stability in the dry expanded state, and

(4) longitudinally contract from the dry expanded state when Wetted withWater at room temperature, said sleeve being rapidly and radiallyshrinkable when wetted with water at room temperature and further beingresistant to tearing, abrasion and fiber disorientation when waterwetted.

References Cited by the Examiner UNITED STATES PATENTS 1,559,785 11/1925Russell 29-120 2,119,491 5/1938 Rapport 29-120 2,133,137 10/1938 Hackett156-86 2,312,853 3/1943 Toland et al.

2,755,516 7/1956 Adams et al. 29127 2,933,130 6/1961 Rittenhouse 2..15686 3,030,696 4/ 1962 Serwer 29127 WALTER A. SCHEEL, Primary Examiner.

EARL M. BERGERT, LOUIS O. MAASSEL, Examiners.

1. A DAMPENING ROLL COVER WHICH CONSISTS OF A SEAMLES, POROUS,HYGROSCOPIC, COHESIVE, WHOLLY NON-WOVEN CYLINDRICAL SLEEVE CONSISTINGESSENTIALLY OF HYDROPHILIC MATERIALS, SAID SLEEVE BEING COMPRISED OFHYDROPHILIC RANDOMLY DISPOSED FIBERS WHICH (1) ARE SUBSTANTIALLY WATERINSOLUBLE AT TEMPERATURES BELOW ABOUT 100*F., (2) CAN BE LONGITUDINALLYEXPANDED WHEN WATER WETTED, (3) HAVE DIMENSIONAL STABILITY IN THE DRYEXPANDED STATE, AND (4) LONGITUDINALLY CONTRACT FROM THE EXPANDED STATEWHEN WETTED WITH WATER AT ROOM TEMPERATURE, SAID SLEEVE FURTHER BEINGRESISTANT TO TEARING, ABRASION AND FIBER DISORIENTATION WHEN WATERWETTED.